1. Field of the Invention
The present invention relates to a technology for adjusting an apparatus for sweep synchronization measurement of optical wavelength sensitivity characteristics, which comprises a wavelength tunable light source and optical power meters, to have flat optical wavelength sensitivity characteristics.
2. Description of the Related Art
FIG. 3 shows an optical component analyzer as a conventional apparatus for performing a measurement contemplated by the invention. The analyzer comprises a wavelength tunable light source 1, an optical output section 2 for outputting light from the wavelength tunable light source 1, an optical input section 3 of a group of optical power meters 4, and a control/computing section 5. A device under test (not shown), which is to be subjected to a measurement, is connected between the optical output section 2 and the optical input section 3. Being controlled by the control/computing section 5, the wavelength sweep of the wavelength tunable light source 1 is synchronized with the power measurement by the optical power meters so as to measure the optical wavelength sensitivity characteristics of the device under test.
The above-described type of instrument combines the wavelength tunable light source with a group of optical power meters and synchronizes the wavelength sweep of the light source with the power measurement by the optical power meters to measure the optical wavelength sensitivity characteristics of the device under test. In such instruments, it is extremely important that flat optical wavelength sensitivity characteristics be maintained in through-measurements which are performed prior tot actual measurements, with no device under test connected.
FIG. 2 is a flowchart for the measurements performed in the conventional art. As shown, the process comprises the following four major steps.
Step 10 in which with no device under test connected between the optical output section 2 and the optical input section 3, through-measurements are performed over the entire wavelength range of measurement at predetermined sampling intervals and the measured values are saved as reference values in an internal memory 6.
Step 11 in which actual measurements are executed with the device under test connected between the optical output section 2 and the optical input section 3.
Step 12 in which the differences between the saved reference values and the actual measured values obtained in step 11 are determined and shown on a display section 7.
Step 13 in which a check is made to see if the conditions for the actual measurements with the device under test connected are varied from those for the through-measurements and if the answer is yes, another cycle of through-measurements is run to determine a new set of reference values.
In order to ensure that flat optical wavelength sensitivity characteristics are maintained in through-measurements, the following sequence of steps have been taken in the conventional art.
First, through-measurements (with no device under test connected) are performed under the same conditions as the measurements to be performed with the device under test connected and their results are saved as reference values in the internal memory 6.
Then, measurements are performed with the device under test connected, the measured values are subtracted from the reference values, and the results of comparison are shown on the display section 7.
Even if no flat optical wavelength sensitivity characteristics were maintained in the through-measurements, the results of the actual measurements with the device under test connected contain the same optical wavelength sensitivity characteristics since they were conducted under the same conditions as the through-measurements. Hence, by subtracting the actual measured values from the results of the through-measurements, the optical wavelength sensitivity characteristics for the through-measurements are effectively cancelled and those of the device under test are correctly shown on the display section 7.
In order to justify the accuracy of the above-described method, the through-measurements must be performed under the same conditions as the actual measurements with the device under test connected. If there is a change in the conditions for the actual measurements with the device under test connected, the previously used reference values (as obtained by the through-measurements) are no longer applicable.
An object, therefore, of the present invention is to ensure that the optical wavelength sensitivity characteristics of a device under test can be measured correctly with an apparatus for sweep synchronization measurement of optical wavelength sensitivity characteristics by maintaining flat optical wavelength sensitivity characteristics during through-measurements.
The stated object of the invention can be attained by an apparatus which corrects the optical wavelength sensitivity of its optical power meters by combination of:
a means of measuring reference values with no device under test connected;
a means of computing a series of corrective values for said reference values at each wavelength such that the measured value at a reference wavelength is zero;
a means of executing the correction of actual measured values using said series of corrective values; and
a means of displaying the actual measured values as corrected.
The apparatus may be modified, wherein if the actual measurements are performed under conditions varied from those for the measurements of reference values, said means of computing a series of corrective values produces a new series of corrective values by arithmetic operations on said varied conditions for the actual measurements and said reference values already measured.
The stated object can also be attained by a method for correcting the optical wavelength sensitivity of optical power meters in an apparatus for sweep synchronization measurement of optical wavelength sensitivity characteristics, which comprises the steps of:
(A) measuring reference values with no device under test connected;
(B) computing a series of corrective values for said reference values at each wavelength such that the measured value at a reference wavelength is zero;
(C) executing the correction of actual measured values using said series of corrective values; and
(D) displaying the actual measured values as corrected.
The method may be modified, wherein the computation of a series of corrective values in step (B) is such that if the actual measurements are performed under conditions varied from those for the measurements of reference values, a new series of corrective values are produced by arithmetic operations on said varied conditions for the actual measurements and said reference values already measured.
The method may also be modified, wherein the computation of a series of corrective values in step (B) is executed by interpolating the series of corrective values.